Surface polysaccharides of pathogenic bacteria, including capsular polysaccharides (CPS) or lipopolysaccharides (LPS),serve both as essential virulence factors and as protective antigens. The age-related and T-cell independent immunogenicity of CPS limit their use as vaccines especially in infants and young children. LPS are too toxic to be administered. Accordingly, their O-specific polysaccharide (O-SP), that share the virulence promoting and protectiveness of CPS, must be purified: O-SP are too small to be immunogenic (haptens). Covalent binding of CPS or of O-SP to medically-useful proteins to form conjugates both increases their immunogenicity and confers T-cell dependence to these saccharides. The O-SP of Shigella sonnei and of S.flexneri 2a were bound to bacterial toxoids. Both conjugates were safe and induced statistically significant and long-lived rises of IgG antibodies to the homologous LPS in adults, 4-7 and 1-4 year-olds. Similar, though lesser rises of IgM and IgA anti-LPS were also induced. Re-injection of S. flexneri 2a conjugate induced a booster response in all age groups,of the S. sonnei conjugate only in the 1-4 year old. A Phase 3 trial showed that one injection of S. sonnei O-SP, bound to a non-toxic recombinant Pseudomonas aeruginosa exoprotein A (rEPA) protected army recruits against outbreaks with this pathogen. Importantly, there was a significant correlation between the levels of serum IgG anti-LPS and the efficacy of the conjugate. Two methods were developed that increased the immunogenicity of the Shigella conjugates in mice: a genetically-inactivated Corynebacterium diphtheriae toxin (CRM9) was a superior carrier for S. sonnei O-SP and treatment of rEPA with succinic anhydride, a non-toxic mild akylating agent that converts amino groups of proteins to carboxyls, increased the immunogenicity of S. flexneri 2a O-SP. A phase 1 study in adults of these Shigella conjugates confirmed their safety and immunogenicity; the improved immunogenicity was less marked than in mice. In a phase 2 study in 1-4 years old the S.flexneri 2a conjugate induced a 4-fold rise in 92% of the children, the S.sonnei conjugate in 85%. A phase 3 study of the modified S.flexneri 2a and the original S. sonnei conjugates are in preparation. In collaboration with the Lanzhou Vaccine Institute and Provincial Medical Center in Henan, China, a clinical trial of these two conjugates is being planned. To investigate if concurrent administration of a cross-reacting along with a homologous CPS has an advantage over the use of the homologous CPS alone, the cell wall polysaccharide (PS) of Bacillus pumilus, SH18, reported to cross react with the CPS of haemophilus influenzae type b (Hib), was isolated by conventional methods and it's structure investigated using GC-MS,NMR, fast atom bombardment and several sugar degrading techniques. It was shown to be composed of polyribitolphosphate bound to polyglycerolphosphate and likely through the latter to the muramic acid of the cell wall. Both polyols are partially substituted at C2 with N-acetylglucosamine.Besides with the anti Hib it cross reacted with anti Staphylococcus epidermidis. The polysaccharide was conjugated to carrier proteins and it's immunogenicity evaluated in GP mice. Conjugate-induced antibodies reacted with the homologous and several cross-reacting polysaccharides. Neisseria meningitidis group A causes endemic and epidemic meningitis, notably in the meningitis belt of Africa. A CPS vaccine , effective and available, is underutilized. To further improve it's immunogenicity it was conjugated to BSA . Contrary to the CPS alone it was immunogenic in mice, with booster responses after 2nd and 3rd injections. Conjugates of the cross reactive polysaccharides, e.coli K93 and B.pumilus SH17,did not induce anti Men. A CPS. Borrelia burgdorferi, a spirochete transmitted though the bite of infected Ixodes ticks, is the etiologic agent of Lyme disease. A protein vaccine against it is available but is not effective below the age of 12 years. LPS has been described in other spirochetes but it's presence in B. burgdorferi has been debated. So far we have not been able to confirm it's presence. The search for LPS revealed a unique glycolipid composed of C16, C18fatty acids possibly glycerol and galactose as the carbohydrate moiety. There is evidence that this glycolipid is surface exposed Injected in complete Freund's adjuvant it induced specific antibodies. The immunogenicity of this glycolipid in various formulations and the biological effect of the antibodies are being ingestigated. Bacillus anthracis, a potential cause of lethal human infection, has 2 essential virulence factors without either of which it is not pathogenic for humans. these factors are: 1.anthrax toxin, 2.a capsule. The toxin is composed of 3 peptides: Lethal Factor, Edema Factor and Protective Antigen, each by itself non toxic. PA is the toxin part that binds to mammalian cells. It has to have a 20 KDa peptide hydrolyzed off exposing a site to which LF or EF may bind rendering toxins that enzymatically modify substrates in mammalian cell cytosol. The capsule is composed of poly-D-gamma-glutamic acid.It is non-immunogenic and it's protective effect unknown. The licensed vaccine is safe and protective but has limitations that justify development of improved vaccines. A recombinant PA was isolated from an unencapsulated strain grown in a fermenter. Several formulations with formaldehyde treated and alum adsorbed materials were found to be immunogenic in mice. Clinical lots are being prepared. The capsule has been isolated from a non toxic strain and methods to conjugate it to carrier proteins are being investigated.